The invention relates to a process for the upgrading of a reaction product obtained in the hydrocarbon synthesis according to Fischer-Tropsch.
In view of the increasing need of liquid hydrocarbon distillates such as gasolines, kerosenes, and gas oils and the decreasing reserves of mineral oil, there is a great interest in processes permitting the conversion, in an economically justified way, of carbon-containing materials not based on mineral oil, such as natural gas and coal, into the above-mentioned liquid hydrocarbon distillates. It is known that carbon-containing materials, such as natural gas and coal can be converted into mixtures of carbn monoxide and hydrogen. It is further known that mixtures of carbon monoxide and hydrogen can be converted into a reaction product containing hydrocarbons and oxygen-containing hydrocarbons by contacting the mixtures at an elevated temperature with a suitable catalyst. In this so-called hydrocarbon synthesis according to Fishcher-Tropsch, a reaction product is obtained in which the hydrocarbons show a very wide spread in carbon number. From the reaction product hydrocarbon mixtures may be separated, the boiling range of which is the same as those of gasolines, kerosenes, and gas oils. A drawback of the reaction product obtained in the hydrocarbon synthesis according to Fischer-Tropsch is that the hydrocarbons present therein are substantially unbranched paraffins. Because of the high content of unbranched paraffins, the hydrocarbon mixtures which may be separated from the reaction product are not very suitable as motor gasolines since they have a low octane number and also not very suitable as fuel for jet engines and diesel engines since they have a high pour point. With regard to the above-mentioned applications, a second drawback of the Fischer-Tropsch reaction product is that it consists to a considerable extent of components boiling below the gasoline range. Finally, the hydrocarbon synthesis according to Fischer-Tropsch has the drawback that part of the mixture of carbon monoxide and hydrogen is converted into oxygen-containing hydrocarbons which are ineligible for the above-mentioned applications.
An investigation by the present applicant concerning the upgrading of a reaction product obtained in the hydrocarbon synthesis according to Fischer-Tropsch has shown that a solution to the above problems can be found by subjecting certain fractions of the reaction product to a conversion using, as the catalyst, certain crystalline silicates which have recently been synthesized for the first time as described in Netherland patent application No. 7,613,957 incorporated herein by reference. It has been found that a considerable upgrading of the fractions concerned is achieved by contacting certain fractions of the reaction product at an elevated temperature with a catalyst which contains one of these crystalline silicates. When the conversion is applied to a light fraction which boils substantially in the gasoline range, an aromatic motor gasoline is obtained. When the conversion is applied to a heavy fraction which boils substantially above the gasoline range, a fuel with a low pour point is obtained. It has further been found that the catalysts are capable of converting a light fraction of the reaction product which boils substantially below the gasoline range into an aromatic motor gasoline. Finally, it has been found that the catalysts are capable of converting oxygen-containing hydrocarbons that are present in the reaction product into hydrocarbons.